The present invention relates to a shock absorber that generates a damping force by controlling a flow of hydraulic fluid during a stroke of a piston rod.
Generally, a shock absorber mounted on a suspension apparatus or the like of a vehicle includes a piston with a piston rod coupled thereto, which is slidably and fittedly inserted in a cylinder sealingly containing hydraulic fluid, and generates a damping force by controlling a flow of the fluid generated by a sliding movement of the piston in the cylinder during a stroke of the piston rod with use of a damping force generation mechanism constituted by a orifice, a disk valve, and the like.
For example, a damping force adjustable shock absorber discussed in International Publication No. 2011/099143 includes a pilot chamber behind a main valve that is a damping force generation mechanism, and a spring element for biasing a pilot valve in a direction for opening a discharge passage from the pilot chamber, and adjusts a damping force by actuating an actuator so as to move the pilot valve in a direction for closing the discharge passage against the biasing force of the spring element to thereby introduce a part of a flow of hydraulic fluid into the pilot chamber to adjust an inner pressure of the pilot chamber.
Further, the spring element is constituted by two members, i.e., a coil spring having a low spring constant and configured to act on the pilot valve during a whole stroke, and a disk spring having a high spring constant and configured to act on the pilot valve only near a seat portion that closes the discharge passage, thereby acquiring a non-linear load-displacement characteristic. In other words, the coil spring allows the spring element to function as a spring for returning the pilot valve to a failure position, and the coil spring and the disk spring allow the spring element to function as a spring for controlling a stroke amount of the pilot valve.